1. Field of the Invention
The invention relates to an audio output system, and more particularly to a multiple output audio system capable of simultaneously playing or switching between different audio sources.
2. Description of the Related Art
FIG. 1 is a schematic block diagram of a dual program audio apparatus in accordance with U.S. Pat. No. 5,910,996. The System 30 intends to receive multiple sources from its input jacks 32a through 32e, and output two of the sources by jacks 33a and 33b. One of the outputs is used as foreground sound which is intended to attract the attention of the listeners, for example, news broadcasting. The other output is used as background sound such as background music which may draw less concentration from the listeners. Dual program amplifier circuit 31 receives as its input signals at input jacks 32a-32e first and second audio programs from a radio tuner A 34, radio tuner B 35, cassette tape player 36, or a compact disc player 37. In an automotive environment car telephone 38 may also be coupled to an input jack 32e. 
Dual program amplifier circuit 31 is coupled to audio speaker sets 39 and 40 via output jacks 33a and 33b, respectively, and comprises switching circuit 41, amplifier A 42 and amplifier B 43. The volume of the audio program output by amplifier A 42 is controlled by volume select circuit 44, while the volume of the audio program output by amplifier B 43 is controlled by volume select circuit 45.
Switching circuit 41 receives and directs the input audio signals via input jacks 32a-32e to amplifier A 42 or amplifier B 43 to drive the audio speaker sets 39 or 40. Although the dual output devices can be driven by the dual program amplifier circuit 31 is easily implemented, the decoding, demodulation or the demultiplexing operation for the input sources 34-38 are independent. The system 30 uses multiple source processors and directs to different output with a multiplexer. Thus, extensive hardware or software resources are required. A multiple output driving system capable of reducing the hardware or software resource loading and having adaptive processing paths is desirable.